Evolution of paraglacial coasts in response to changes in fluvial sediment supply

Abstract

Paraglacial coastal systems are formed on or proximal to formerly ice-covered terrain from sediments with direct or indirect glacial origin. This review addresses the roles of tectonic controls, glacial advances and retreats, sea-level changes, and coastal processes in sediment production, delivery and redistribution along the paraglacial Gulf of Maine coast (USA and Canada). Coastal accumulation forms are compositionally heterogeneous and found primarily at the seaward edge of the Gulf's largest estuaries; their existence is directly attributable to the availability of glacial sediments derived from erosion of weathered plutons within coastal river basins. Multiple post-glacial sea-level fluctuations drove the redistribution of these sediments across the modern lowland and inner shelf. Central to the formation of barrier systems was the paraglacial sand maximum, a time-transgressive phase of relative sea-level fall and enhanced fluvial sand export c. 2000–4000 years following deglaciation. Vast quantities of sand and gravel were reworked landward during the subsequent transgression and combined with additional riverine sediments to form the modern barrier systems. Today, reduced fluvial sediment loads, anthropogenic modifications of barrier and river systems, and sea-level rise have combined to exacerbate long-term coastal erosion and may eventually force these barriers toward a state of rapid landward migration.

Longshore Sediment Transport Directions and Rates from Northern Maine to Tampa Bay, Florida: Literature Compilation and Interpretation

“…Great property losses in the vicinity of the jetty led local people to complain about the structure, which has long since outlived its original industrial purpose and resulted in numerous studies of the sand movement in the bay by ourselves and a number of colleagues. In a series of theses (Barber, 1995;Brothers, 2006;Heinze, 2001;Manthorp, 1995;van Heteren, 1996) and peer-reviewed papers (Brothers et al, 2008;Buynevich, FitzGerald, and van Heteren, 2004;FitzGerald et al, 2000FitzGerald et al, , 2002FitzGerald et al, , 2005Hein et al, 2014;Hill et al, 2004;Kelley and Anderson, 2000;Kelley et al, 2005;Kelley and Brothers, 2009;van Heteren et al, 1996), we established that sand moves in a net northerly direction in the bay. The Army, after performing physical (Bottin, Mize, and Demirbilek, 1995) and numerical (Woods Hole Group Environmental Laboratories, 2006) modeling agreed with our field measurements.…”

General considerations and highlights of low-lying coastal zones: passive continental margins from the poles to the tropics

“…More sand allows for the generation of large coastal dune systems. The result is that many modern sandy beaches of the paraglacial temperate zone do not significantly differ morphologically and structurally from those of warmer areas (Hein et al 2014). However, their stratigraphic position above glacigenic landforms and polymictic deposits still reveals their paraglacial settings.…”

“…Coastal beaches, bars and barriers of cold paraglacial areas are more frequently composed of coarser clasts than those of warmer zones. However, after deglaciation the surficial glacial and periglacial deposits are reworked by fluvial and coastal processes and winds, and given sufficient time, sorting can occur, rendering them morphologically and texturally similar to those of warmer climatic zones (Hein et al 2014).…”

Insight into the late Holocene sea-level changes in the NW Atlantic from a paraglacial beach-ridge plain south of Newfoundland

“…Moreover, the rate of RSL rise at Saint-Pierre-etMiquelon over the period of barrier formation is similar to rates reported during the period for development of similar systems (barriers or beach ridge plains) in the northwest Atlantic. For example, formerly transgressive barriers stabilized and began prograding in the western Gulf of Maine (Plum Island, Massachusetts) and along the Outer Banks barrier island chain (Bogue Banks, North Carolina) as RSL rise rates slowed to < 1.5 mm/yr and 0.8 mm/yr, respectively (Timmons et al, 2010;Hein et al, 2014a). Likewise, these rates were < 1.4 mm/yr on the south coast of New Brunswick (Bay of Fundy) (Gehrels et al, 1996; and < to 2 -2.4 mm/yr at Halifax (Nova Scotia) over the last 3000 years (Scott et al, 1995).…”